DESPITE extensive research and development of different types of artificial oxygenators, the actual capabilities of present designs do not approach closely enough the requirements of the ideal oxygenator, and much remains to be accomplished in this field. Although many important improvements have been made in the recent past, the problems of destruction of the formed elements of the blood and denaturation of plasma proteins are yet to be overcome. Many types of pump-oxygenators are now available which are capable of assuming complete pulmonary function for limited periods without causing extensive damage to the blood. Such units are sufficiently gentle in their treatment of blood so that massive denaturation of plasma proteins and damage to the red cells occurs after extended periods of artificial circulation.4,6,9 It is the latter which presents the most serious problem, particularly in consideration of prolonged partial bypass as might be used for failure of the